The present invention is directed generally to an apparatus for conveying cut or fan-fold paper in a printer, and, in particular, to a paper feeder which prevents slack from developing in the paper as it is conveyed in both the reverse and forward directions through the printer.
A conventional apparatus for conveying cut paper in a printer is shown in FIG. 1. The printer includes a print head 1. Cut paper 13 is fed downstream in the direction of arrow A to print head 1. A pair of paper conveying rollers 14 are positioned upstream of print head 1 and a platen 12. Cut paper 13 is fed by a pair of paper discharging rollers 11 positioned downstream of print head 1 and platen 12 in conjunction with paper conveying rollers 14. Paper discharging rollers 11 rotate at a faster speed than paper conveying rollers 14 to take up any slack that occurs across cut paper 13.
Another conventional paper feeding apparatus is shown in FIG. 2 for feeding fan-fold paper in a printer. The device includes a print head 2 and an opposed platen 22. A push tractor 24 feeds fan-fold paper 23 downstream in the direction of arrow A (the forward conveying direction) to print head 2 and platen 22. A pair of sheet conveying rollers 25 are positioned upstream of print head 2. Fan-fold paper 23 is conveyed by sheet discharging rollers 21 in cooperation with paper conveying rollers 25.
Paper discharging rollers 21 rotate at a greater peripheral speed than paper conveying rollers 25 so that fan-fold paper 23 is stretched tight between paper discharging rollers 21 and paper conveying rollers 25 and between tractor 24 and paper conveying rollers 25.
The above-described conventional paper feeders for printers suffer from the following difficulties when the printing sheet is conveyed in the reverse direction (in the direction of arrow B). Referring specifically to FIG. 1, when cut paper 13 is conveyed by sheet discharging rollers 11, platen 12 and paper conveying rollers 14 in the direction of arrow B (the reverse conveying direction), slack occurs on cut paper 13 between paper discharging rollers 11 and paper conveying rollers 14 because the peripheral speed of paper discharging rollers 11 is greater than that of paper conveying rollers 14. The resultant slack causes degradation in printing accuracy.
In the embodiment of FIG. 2, tractor 24, platen 22, paper conveying rollers 25 and paper discharging rollers 21 convey fan-fold paper 23 in the printer. As described above with respect to FIG. 1, when conveying fan-fold paper 23 in the reverse direction, slack develops on fan-fold paper 23 between paper discharging rollers 21 and paper conveying rollers 25 so that fan-fold paper 23 may be caught in the printer. Furthermore, since the peripheral speed of paper conveying rollers 21 is greater than that of paper conveying rollers 25, the slack causes fan-fold paper 13 to jam and separate from tractor 24. In addition, the back-out capacity is lowered.
Accordingly, it is desired to provide an apparatus for conveying paper which overcomes the disadvantages of the prior art devices described above by providing a conveying mechanism which eliminates slack during conveying in the reverse direction by applying tension to the paper when conveyed in either a forward or reverse direction.